2,721 research outputs found
Pulsar wind nebulae in supernova remnants
A spherically symmetric model is presented for the interaction of a pulsar
wind with the associated supernova remnant. This results in a pulsar wind
nebula whose evolution is coupled to the evolution of the surrounding supernova
remnant. This evolution can be divided in three stages. The first stage is
characterised by a supersonic expansion of the pulsar wind nebula into the
freely expanding ejecta of the progenitor star. In the next stage the pulsar
wind nebula is not steady; the pulsar wind nebula oscillates between
contraction and expansion due to interaction with the reverse shock of the
supernova remnant: reverberations which propagate forward and backward in the
remnant. After the reverberations of the reverse shock have almost completely
vanished and the supernova remnant has relaxed to a Sedov solution, the
expansion of the pulsar wind nebula proceeds subsonically. In this paper we
present results from hydrodynamical simulations of a pulsar wind nebula through
all these stages in its evolution. The simulations were carried out with the
Versatile Advection Code.Comment: 10 pages, 9 figures, submitted to Astronomy and Astrophysic
F and D Values with Explicit Flavor Symmetry Breaking and \Delta s Contents of Nucleons
We propose a new model for describing baryon semi-leptonic decays for
estimating and values with explicit breaking effects of both SU(3) and
SU(2) flavor symmetry, where all possible SU(3) and SU(2) breaking effects are
induced from an effective interaction. An overall fit including the weak
magnetism form factor yields and with
d.o.f. with and . The spin content of strange quarks is estimated from the
obtained values and , and the nucleon spin problem is re-examined.
Furthermore, the unmeasured values of and for other hyperon
semi-leptonic decays are predicted from this new formula.Comment: 15 pages, 1 figure, final version to appear in PR
Financial correlations at ultra-high frequency: theoretical models and empirical estimation
A detailed analysis of correlation between stock returns at high frequency is
compared with simple models of random walks. We focus in particular on the
dependence of correlations on time scales - the so-called Epps effect. This
provides a characterization of stochastic models of stock price returns which
is appropriate at very high frequency.Comment: 22 pages, 8 figures, 1 table, version to appear in EPJ
The particle spectrum of the Tricritical Ising Model with spin reversal symmetric perturbations
We analyze the evolution of the particle spectrum of the Tricritical Ising
Model by varying the couplings of the energy and vacancy density fields. The
particle content changes from the spectrum of a supersymmetric theory (either
of an exact or a spontaneously broken supersymmetric theory) to the spectrum of
seven particles related to the underlying E_7 structure. In the low temperature
phase some of these excitations are topologically charged particles that are
stable under an arbitrary variation of the parameters. The high and low
temperature phases of the model are related by duality. In some regions of the
two couplings there are also present false vacua and sequences of bound states.
In order to study the non-integrable features of this model we employ the Form
Factor Perturbation Theory and the Truncated Conformal Space Approach.Comment: 34 pages, 14 figures, text misprints correcte
Three-sublattice ordering of the SU(3) Heisenberg model of three-flavor fermions on the square and cubic lattices
Combining a semi-classical analysis with exact diagonalizations, we show that
the ground state of the SU(3) Heisenberg model on the square lattice develops
three-sublattice long-range order. This surprising pattern for a bipartite
lattice with only nearest-neighbor interactions is shown to be the consequence
of a subtle quantum order-by-disorder mechanism. By contrast, thermal
fluctuations favor two-sublattice configurations via entropic selection. These
results are shown to extend to the cubic lattice, and experimental implications
for the Mott-insulating states of three-flavor fermionic atoms in optical
lattices are discussed.Comment: 4 pages, 3 figures, minor changes, references adde
Density matrix numerical renormalization group for non-Abelian symmetries
We generalize the spectral sum rule preserving density matrix numerical
renormalization group (DM-NRG) method in such a way that it can make use of an
arbitrary number of not necessarily Abelian, local symmetries present in the
quantum impurity system. We illustrate the benefits of using non-Abelian
symmetries by the example of calculations for the T-matrix of the two-channel
Kondo model in the presence of magnetic field, for which conventional NRG
methods produce large errors and/or take a long run-time.Comment: 12 pages, 6 figures, PRB forma
Phase field theory of interfaces and crystal nucleation in a eutectic system of fcc structure: I. Transitions in the one-phase liquid region
The published version of this Article can be accessed from the link below - Copyright @ 2007 American Institute of PhysicsThe phase field theory (PFT) has been applied to predict equilibrium interfacial properties and nucleation barrier in the binary eutectic system Ag-Cu using double well and interpolation functions deduced from a Ginzburg-Landau expansion that considers fcc (face centered cubic) crystal symmetries. The temperature and composition dependent free energies of the liquid and solid phases are taken from CALculation of PHAse Diagrams-type calculations. The model parameters of PFT are fixed so as to recover an interface thickness of approximately 1 nm from molecular dynamics simulations and the interfacial free energies from the experimental dihedral angles available for the pure components. A nontrivial temperature and composition dependence for the equilibrium interfacial free energy is observed. Mapping the possible nucleation pathways, we find that the Ag and Cu rich critical fluctuations compete against each other in the neighborhood of the eutectic composition. The Tolman length is positive and shows a maximum as a function of undercooling. The PFT predictions for the critical undercooling are found to be consistent with experimental results. These results support the view that heterogeneous nucleation took place in the undercooling experiments available at present. We also present calculations using the classical droplet model classical nucleation theory (CNT) and a phenomenological diffuse interface theory (DIT). While the predictions of the CNT with a purely entropic interfacial free energy underestimate the critical undercooling, the DIT results appear to be in a reasonable agreement with the PFT predictions.This work has been supported by the Hungarian Academy of Sciences under Contract No. OTKA-K-62588 and by the ESA PECS Contract Nos. 98005, 98021, and 98043
Dynamical conductance in the two-channel Kondo regime of a double dot system
We study finite-frequency transport properties of the double-dot system
recently constructed to observe the two-channel Kondo effect [R. M. Potok et
al., Nature 446, 167 (2007)]. We derive an analytical expression for the
frequency-dependent linear conductance of this device in the Kondo regime. We
show how the features characteristic of the 2-channel Kondo quantum critical
point emerge in this quantity, which we compute using the results of conformal
field theory as well as numerical renormalization group methods. We determine
the universal cross-over functions describing non-Fermi liquid vs. Fermi liquid
cross-overs and also investigate the effects of a finite magnetic field.Comment: 11 pages in PRB forma
Detection of multipartite entanglement with two-body correlations
We show how to detect entanglement with criteria built from simple two-body
correlation terms. Since many natural Hamiltonians are sums of such correlation
terms, our ideas can be used to detect entanglement by energy measurement. Our
criteria can straightforwardly be applied for detecting different forms of
multipartite entanglement in familiar spin models in thermal equilibrium.Comment: 5 pages including 2 figures, LaTeX; for the proceedings of the DPG
spring meeting, Berlin, March 200
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